1. Incorporation by Reference
The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application Nos. 2003-053059 filed on Feb. 28, 2003 and 2003-056639 filed on Mar. 4, 2003. The contents of the applications are incorporated herein by reference in their entirety.
2. Field of the Invention
The present invention relates to a Cermet cutting tool having a coated surface (to be referred to as a coated Cermet cutting tool) used for high-speed, intermittent cutting of various types of steel, cast iron and so forth, and its hard coating layer in particular demonstrates superior chipping resistance.
3. Description of the Related Art
Known examples of coated Cermet cutting tools comprise a base (to be generically referred to as the tool base) made of tungsten carbide (WC)-based cemented carbide or titanium carbide (TiC)-based Cermet, and a hard coating layer. This hard coating layer comprises:    (a) a Ti compound and/or Zr compound layer, which is a lower layer, comprising one or more layers of a Ti carbide (TiC) layer, Ti nitride (TiN) layer, Ti carbonitride (TiCN) layer, Ti oxicarbide (TiCO) layer, Ti oxicarbonitride (TiCNO) layer, Zr carbide (ZrC) layer, Zr nitride (ZrN) layer, Zr carbonitride (ZrCN) layer, Zr oxicarbide (ZrCO) layer and Zr oxicarbonitride (ZrCNO) layer formed by chemical vapor deposition (to be simply referred to as vapor deposition formation), and having an overall mean layer thickness of 0.5–20 μm, and    (b) an aluminum oxide layer having an α crystal structure in the vapor deposited state (to be referred to as an α-Al2O3 layer), which is an upper layer, and having a mean layer thickness of 1–30 μm.
These coated Cermet cutting tools are widely known to be used for continuous and intermittent cutting of various types of steel, cast iron and so forth.
In addition, Japanese Unexamined Patent Application, First Publication No. Hei 6-31503 discloses that the Ti compound layer and the α-Al2O3 layer, which compose a hard coating layer, have a particulate crystal structure.
Moreover, Japanese Unexamined Patent Application, First Publication No. Hei 6-8010 discloses a technology for improving the strength of a TiCN layer comprising the Ti compound layer in which the TiCN layer is made to contain a longitudinally growing crystal structure by vapor deposition with an ordinary chemical vapor deposition device in an intermediate temperature range of 700–950° C. using a mixed gas containing organic carbonitride as the reactive gas.
Cutting devices have recently come to be required to offer higher performance, and there are also strong needs for saving of labor, saving of energy and reduced costs with respect to cutting processing. Accompanying these needs, the speed of cutting processing is tending to become even faster, resulting in the unavoidable circumstances of cutting processing under heavy-duty cutting conditions including greater cutting depth and faster feeding.
There are no problems with the use of the conventional coated Cermet cutting tools in the case of continuous or intermittent cutting of steel or cast iron and so forth under ordinary conditions. However, although the α-Al2O3 layer that composes the hard coating layer has superior heat resistance, since it is not provided with adequate strength, when used for high-speed intermittent cutting under severe cutting conditions, namely high-speed intermittent cutting in which thermal shock is repeatedly applied at an extremely short pitch to the cutting edge, chipping occurs easily in the hard coating layer. As a result, the cutting tool reaches the end of its service life in a comparatively short period of time.